The present invention generally relates to compressors. More particularly, the present invention relates to a rotary compressor having a new structure which increases performance, improves reliability, simplifies assembly procedures, and minimizes the compressor size.
Existing rotary compressors typically comprise a housing, an electric motor with a motor stator secured to the inside wall of the housing by shrink fitting, an internal motor rotor permanently fixed to an unsupported end of a revolving crankshaft to rotatable engaged with the motor stator, said revolving crankshaft extended axially to a mounted below or above the electric motor a pump, which is supported in the housing by welding the pump side or its bearing portion to the wall of the housing at a plurality of points. The pump generally comprises a stationary cylinder block having a bore therein, rigidly fixed to the cylinder block stationary cylinder heads with bearings supporting journalled crankshaft, cylindrical roller precisely mounted around an eccentric section of the revolving crankshaft, sliding vane separating suction space from discharge one and arranged in vane slot located in the wall of the stationary cylinder block between a suction port and a discharge port. A tip end portion of the sliding vane is always put in contact with part of an outer peripheral surface of the rotating roller by force of a back pressure of the discharge gas and a spring.
In the compressor constructed as described above, the motor unit and the compression unit are installed axially with a predetermined distance there between. This distance combined with height of the motor and height of the pump defines as an axial length of the compressor so a transmission loss of the rotating power generating by the motor and distributed to the pump by revolving crankshaft. Any increase of the distance will enlarge the size of the compressor and maximize the transmission loss of the rotating power.
The parts of a prior art rotary compressor are supported as by crankshaft (rotor, roller, etc.), so by the housing (stator, pump, external suction accumulator, etc.). Such dual supporting structure complicates assembly of a compressor due to the necessity of precision axial and radial positioning of the parts. The bore of the stationary cylinder block has to be concentric with the revolving crankshaft and therefore needs to be aligned very precisely as with the crankshaft, so with the revolving crankshaft bearings and the motor rotor. Since in the prior art structures the motor stator and the stationary cylinder block are attached to the housing, the position of the motor rotor has to be aligned with both. It is crucial that the bearings formed in the stationary cylinder heads are aligned with both the motor stator and the stationary cylinder block in order to prevent excessive gaps between an external wall of the roller and periphery of the cavity formed in the stationary cylinder block. Furthermore, distortion can occur in the cylinders vane slot during the welding of the cylinder block to the housing, thereby causing loss of the vane-vane slot clearance and following intensive wear of the contacting surfaces or failure of the compressor.
Attachment of the motor stator has generally been accomplished by shrink fitting and, therefore, the stationary cylinder block and the motor stator have their entire perimeter in contact with the internal perimeter of the housing which has to be machined to have even cylindrical surface. Furthermore, the internal surface of the stator tends to be uneven and eccentric relative to the outer surface thereof due to the laminated construction of the motor stator. When the motor and the pump are assembled together with reference to the internal surface of the housing, the central axis of the motor rotor tends to be inclined against the internal surface of the motor stator. The above described misalignment causes an air gap between the motor stator and the motor rotor to be uneven. When the air gap is uneven, the motor rotor of the motor is urged by magnetic force toward a side of the stator having a narrower air gap, thus increasing load on the crankshaft bearings and maximizing the starting torque of the motor. The housing surface also tends to be deformed from a true cylindrical configuration as a result of welding of end caps, the stationary cylinder block, fittings of discharging and suction pipes, etc., thus changing an established stator-rotor air gap.
The cantilevered position of the motor rotor on the unsupported end of the revolving crankshaft, limitation of the crankshaft diameter by the compressor structure, and large variable gas force affecting the eccentric part of rotating crankshaft, deflect the crankshaft and make the bearings load relatively high. Additional load due to an uneven air gap promotes slanting abrasion of the bearings and increases possibility of a contact between the top edge of the rotor and inner surface of the stator. This phenomenon affects the reliability of the compressor.
The eccentric part of a crankshaft (due to the deflection phenomena) induces a centrifugal inertia force that causes rotational imbalance associated with the problem of noise and vibration of a compressor. The traditional solving method is to add a pair of balancers in the upper and lower side of the motor rotor, considering the revolving crankshaft to be rigid. However, when such traditional method is applied to the inverter controlled compressors (rotation speed more than 3000 rev/min), the level of noise and vibration is not ideal.
Contacting surfaces of the pump parts are subjected to higher wear, and they require as precision machining so extremely close tolerances, which are generally on the order of ten thousands of an inch. Axial and radial clearances between working parts induce internal leakage flow and associated leakage losses which, in combination with frictional losses, have great impact on performance and reliability of the compressor. The leakage and frictional losses in contemporary rotary compressors are due to an operating clearances between the contacting surfaces of the following parts: roller O.D—vane tip, roller O.D.—stationary cylinder I.D., roller I.D.—crankshaft eccentric, roller axial ends-facing stationary cylinder heads surfaces, vane axial ends-facing stationary cylinder heads surfaces, vane sides-stationary cylinder block slot sides, revolving crankshaft-stationary bearings. The contemporary rotary compressors have the rollers' axial and radial surfaces sliding 360° against the surfaces of stationary end wall of the cylinder block and heads. The sliding vane tip forced against the roller end wall by combine load of a spring and a discharge back pressure is main contributor to the friction losses due to practically grinding contact with the roller and continuous sliding of the vane against stationary walls of the cylinder heads and sides of the vane slot significantly increase frictional losses. An additional leakage of the flow is through the clearances, which are necessary for the vane reciprocating movement. Precision machining is necessary for the prior art compressor parts to reduce frictional and internal leakage losses.
The contact between roller O.D. and vane tip (and associated frictional losses) has been eliminated in the conventional swing type rotary compressors due to the design of roller and vane as one part. However, frictional and leakage losses are high due to an increase areas of roller-integral vane radial ends surfaces facing stationary cylinder heads.
Furthermore, in the prior art compressors, the suction gas is generally supplied from a suction accumulator, which is externally attached to the compressor housing. Primarily, the accumulator receives and accumulates the vapor-liquid mixture from evaporator of the unit and serves as a reservoir and separator of the liquid, gas and oil. The output tube of the accumulator passed through a hole in the housing and requires an inline hole which has to be precision positioning in the wall of the cylinder block. This tube is in direct communication with the suction chamber. However, with direct delivery of a vapor-liquid mixture to a suction chamber, there can be a problem with slugging. Slugging is a condition that occurs when a mass of liquid, here from accumulator, enters the suction chamber. This liquid, when in sufficient volume and being essentially incompressible, adversely affects the operation of the compressor and can cause severe damage.
Still another problem associated with prior art hermetic compressor arrangements is that the resistance to incoming suction gas from the accumulator is high, generally a resistance co-efficient of at least 0.5. The suction port acts as a throttle and the pressure drop across the accumulator (a critical system efficiency parameter) is high due to the resistance to the suction gas flow.
Since the accumulator is mounted in a close proximity to the compressor housing, any heat and vibration generated by the compressor and the unit will be transmitted directly to the accumulator. The combined load of the pressure pulsations and vibrations triggered by operation of the compressor and associated unit will stress the joints between the housing and the accumulator output tube, the accumulator inlet and the evaporator output conduit and is sometimes sufficient to fatigue and damage the individual components. Due to the fact that an accumulator has large radiation surface area, its contribution to a compressor noise is substantial. An accumulator noise generation mechanism includes structural vibrations transferred through connecting tubing as from the compressor side, so from the unit side and an accumulator cavity acoustic resonances excited by suction pressure.
The proximity of the accumulator to the hot housing and its external positioning helps transfer heat to the suction gas as from the compressor, so from surrounding environment. The overheating of the gas being drawn causes an increase in the specific volume and, consequently, a reduction of the refrigerant mass flow. Since the refrigerating capacity of the compressor is directly proportional to the mass flow, reducing said flow results in efficiency loss. Furthermore, moisture condensation on a surface of the accumulator and connecting tubing triggers corrosion, which can damage the suction system. In addition, the complexity and dimensions of the accumulator (very often ⅔ of the compressor size) drastically increases the compressor cost and maximize a necessary package space.
In operation of a rotary compressor, as roller revolves inside the stationary cylinder bore when the crankshaft rotates, refrigerant enters the bore through suction port. As the volume enclosed by vane, roller and the wall of bore is reduced in size by the rolling action of the roller, refrigerant will be compressed and will be discharged from the cylinder bore through discharge valve into an inner space of the housing, than flows through rotor-stator air gap and discharge tube toward a unit. An elevated temperature of the discharge gas-oil mixture and high pressure pulsation may provide inadequate cooling of the motor. Such an electric motor operating conditions during long operating cycles will cause overheating of the motor stator winding and can lead to premature motor failure.